A spectrometer is an analytical instrument in which an emission (e.g., particles or radiation) is dispersed according to some property of the emission (e.g., mass or energy), and the amount of dispersion is then measured. Analysis of the dispersion measurement can reveal information regarding the emission, such as the identity of the individual particles of the emission.
One type of spectrometer is a mass spectrometer, which can be used to determine the chemical composition of substances and the structures of molecules. One type of mass spectrometer is a time-of-flight (TOF) mass spectrometer, which records the mass spectra of compounds or mixtures of compounds by measuring the time (e.g., in tens to hundreds of microseconds) for molecular and/or fragment ions of those compounds to traverse a drift region within a high vacuum environment. TOF mass spectrometers operate based on the principle that, when ions are accelerated with a fixed energy, the velocity of the ions depend exclusively on mass and charge. Thus, the time-of-flight of an ion drifting from point A to point B will differ depending on the mass of the ion. Using a TOF mass spectrometer, the mass of an ion can be calculated based upon its time of flight. This allows the molecule to be identified with precision.
TOF mass spectrometers are comprised of a source region, where neutral molecules are ionized, a drift region, followed by an ion reflector (also known as a reflectron) and a detector. The ion source provides a high vacuum environment in which ions are formed, and the ions are subsequently accelerated into a drift region (which may be field-free). The ions separate in time, depending only on their mass/charge ratio (the ion charge is often +1). Upon entering the opposing field created by the reflectron, the ions gradually slow down until they ultimately stop and reverse direction. Ion detection occurs after the ions are re-accelerated back out of the reflectron. In addition to enabling the calculation of the mass of the ions, ion packet peak widths are sharpened by their passage through the reflectron, resulting in an enhancement of the instrument's resolving power.
Reflectrons have been in use since the late 1960's and are typically constructed by configuring a series of individually manufactured metallic rings along ceramic rods using insulating spacers to separate each ring from the next. This technique is labor intensive, costly, and limits the flexibility of design due to the manufacture and handling of extremely thin rings (e.g., a few mils in thickness) of relatively large diameter (often 1″ or greater). An example of such a configuration is shown in U.S. Pat. No. 4,625,112 to Yoshida, which is hereby incorporated herein by reference.
The rings are often placed at potentials that develop uniform electric fields along the axis of the cylinder. However, to improve performance in a TOF mass spectrometer, reflectrons have also been constructed which develop non-uniform fields along the reflectron tube. The non-uniform fields are generated by utilizing a voltage divider network which varies the potential applied to each of the evenly-spaced rings. A detailed explanation of non-linear reflectron theory can be found in U.S. Pat. No. 5,464,985 to Cornish, et al., which is hereby incorporated in its entirety herein by reference.
Additional examples of reflectrons and TOF mass spectrometry theory can also be found in U.S. Pat. No. 6,013,913 to Hanson, U.S. Pat. No. 6,365,892 to Cotter, et al., and U.S. Pat. No. 6,607,414 to Cornish, et al., each of which is hereby incorporated herein by reference.
While the above-described TOF mass spectrometer design has proved quite satisfactory for large reflectors in which the rings are relatively large in diameter and equally spaced, new applications utilizing remote and/or mobile TOF mass spectrometers may require miniaturized components, rugged construction, and/or lightweight materials.